Toda Kogyo Corporation

Akira Mukaizaka

Akio Mishima

Tosiharu Harada

Tomoyuki Imai

Hiroshi Sumita

Yoshiro Okuda

Yosiro Okuda

Hiroyuki Kondo

Nanao Horiishi

Tokihiro Kurata

Goro Matsui

Atushi Takedoi

Yoshitaka Yoshinaga

Disclosed herein is spindle ferromagnetic alloy particles having the aspect ratio (major:minor) of less than 3:1 and the coercive force of 500 to 100 Oe, and containing 0.1 to 13 atomic % of Si to Fe, and a process for producing the same.

Spindle ferromagnetic alloy particles

Disclosed herein is acicular ferromagnetic alloy particles for magnetic recording, containing Si, Cr, Ni and P and optionally Mg impregnated with phosphorus compound and silicon compound and process for producing the same.

Acicular ferromagnetic alloy particles for magnetic recording and

Acicular ferromagnetic alloy particles doped with silicon, chromium and nickel and optionally magnesium and a process for producing said particles comprising heating at 300.degree. to 500.degree. C. under reducing atmosphere acicular particles of .alpha.-iron(III) oxide hydroxide doped with silicon, chromium and nickel and optionally magnesium or acicular particles of .alpha.-ferric oxide doped with silicon, chromium and nickel and optionally magnesium obtained by dehydrating the acicular particles of .alpha.-iron(III) oxide hydroxide doped with silicon, chromium and nickel and optionally magnesium are disclosed herein.

Acicular ferromagnetic alloy particles and process for producing said

A process for producing an acicular ferromagnetic alloy particles mainly containing iron and magnesium, which comprises preparing a suspension of iron(II) hydroxide and water-soluble magnesium salt, the suspension having a pH value of at least 11 and containing the magnesium salt in an amount of 0.5 to 20.0 atomic % based on the amount of the iron(II) hydroxide in the suspension and calculated as the ratio of Mg to Fe(II), oxidizing the suspension with an oxygen-containing gas to form an acicular particles of iron(III) oxide hydroxide substituted with magnesium, forming coats of phosphorus compound and subsequent silicon compound on the acicular particles, heating the resultant particle at 500.degree. to 900.degree. C. under a non-reducing atmosphere and then reheating the particle thus treated at 350.degree. to 600.degree. C. under reducing atmosphere.

Process for producing acicular ferromagnetic alloy particles and

Fine magnetic particles with high saturation magnetization (over 140 emu/g) as well as high stability against oxidation in air, are produced by a process which comprises the first stage of oxidizing the surfaces of metallic particles consisting mainly of iron in an atmosphere containing both H.sub.2 O and H.sub.2 gases at an oxidizing temperature below 900.degree. C., and the second stage of further oxidizing the surfaces of the particles produced at the first stage in an atmosphere containing O.sub.2 gas.

Process for preparing magnetic particles with metallic region therein,

A process for treating acicular magnetite containing Co to stabilize the magnetic properties thereof comprises the steps of heating acicular magnetite containing 0.1 to 2.5% by atom of Co with respect to Fe as starting material at a temperature in the range of 300 - 1000.degree. C in an inert gas atmosphere in which the partial pressure of oxygen is controlled at a value in the range of 0.001 - 1% by weight and for the time sufficient to homogenize the crystal structure of the acicular magnetite by thermal-diffusion of oxygen thereinto, and thereafter saturating the resultant acicular magnetite with oxygen by heating it at a temperature in the range of 40 - 100.degree. C in an oxygen rich atmosphere such as air.

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Hiroshima, Japan

Akira Mukaizaka